1. Field of the Invention
This invention relates to measurement of light and illumination and the performances of digital or analogue cameras such as sensitivity and signal waveforms, signal to noise ratio, resolution and spectrum.
2. Description of Prior Art
The performances of CCTV, Web cameras and other television and digital cameras are measured in laboratories by a variety of test equipment, such as illumination meters, waveform oscilloscope, vectorscope and signal to noise meter by using standard illuminators, light boxes and charts. Normally, the conditions under which the measurements should or are performed are laboratory environment as defined, for a given performance measurement, by national or international institutions such as EIA, ISO, CCIR, SMPTE or other standards. For example signal to noise ratio is measured with the camera exposed to equally distributed 2000 Lux over a reflecting white plane.
Such measurements under controlled environment are proper, however because many of the inter-relations between light, illumination, bandwidth, noise and signal levels are not specified or subject to a cover-all standard, the potential users of such cameras cannot accurately comprehend the performance on the basis of the printed specifications, particularly when the specified figures relate to an unknown and/or undefined scene environment or scene content. Thus, the only practical references available to the potential users for selecting a camera are the comparisons between the published data sheets by the different manufacturers, the result of which is that the performances of cameras in the field do not match the user's expectation.
This gap between user's expectation and the actual performance of purchased cameras causes confusion and bewilderment. Moreover, the confusion caused by misinformation as to the true performance of cameras, as referred to in the camera's data sheets and specified figures of performances, are practically impossible to verify. This persisting state of misinformation enabled some manufacturers to take advantage of the market by publishing non-realistic performance figures. To avoid legal and other challenges, the non-realistic performances are commonly conditioned on complex terms and terminologies known only to professionals in the camera field. The result of all this is that many cameras are specified in catalogs and data sheets with unrealistic performance figures which causes great harm and losses to the unsuspecting users of security and similar cameras.